1. Field of the Invention
The present invention relates to a plasma processing apparatus for performing processings such as etching, film-formation, and ashing of a processing-target object by generating plasma using a high-frequency wave.
2. Description of the Related Art
The miniaturization and high-integration implementation of ULSI devices have been developed rapidly. For example, the device machining whose machining dimension is equal to a few tens of nanometers is now being carried out. Also, large-diameter implementation of the φ-300-nm wafer is now being developed. Namely, the high-accuracy implementation and large-diameter accomplishment are requested at present. Of them, since the gate machining is an important factor which rules operation speed and integration scale of the devices, its machining dimension critical-dimension (CD) is requested most severely. Simultaneously, new materials, such as multilayered film and metal gate, have come to be used as the gate structure. The difference in the machined film type requires a difference in the gas to be used. Accordingly, distribution of the plasma or radical also varies in accompaniment therewith. Also, accomplishing an enhancement in the machining throughput requires high-density implementation of the plasma. One method therefor is high-frequency implementations of the excitation frequency. Of these implementations, the plasma processing apparatus using a μ wave is widely used at present. This is because the plasma generation is executable in the used process area ranging from an about 0.1-Pa low-pressure area to an about 10-Pa high-pressure area, and because the high-density implementation related with the throughput is easy to accomplish. On the other hand, however, the use of the μ wave causes eigen “modes” to rise which are determined by its introduction method and the apparatus size. As a result, there exists a problem that the μ wave is likely to become nonuniform in the radial and circumferential directions. As a method for solving this problem, various types of antennas and slots have been considered from conventionally. This method, however, finds it difficult not only to eliminate electric-field distributions of near fields radiated from the various types of antennas and slots, but also to eliminate the eigen modes caused to rise in the apparatus size.
As a method which, of the eigen modes, eliminates the nonuniformity in the circumferential direction, there exists a method of introducing a circularly polarized wave. The circularly polarized wave refers to an electromagnetic wave whose electric-field direction rotates one turn during one period within a plane perpendicular to a traveling direction of the electromagnetic wave. As its example, the disclosure has been made in a cited embodiment in JP-A-2003-188152 concerning a method where a circularly polarized wave converter is combined with a cylindrical waveguide. As the circularly polarized wave converter, there exists a one where, as illustrated in FIG. 16 in the cited conventional embodiment 1, mutually-opposed and metallic circular-cylinder-shaped stubs 591A and 591B are provided in one pair or plural pairs on inner wall of the cylindrical waveguide 541. The stubs forming the one pair are located in a direction which forms 45° with respect to the main direction of the electric field of a linearly polarized wave TE11 mode to be introduced. When the stubs are provided in the plural pairs, the stubs are located with a spacing of λg/4 (λg denotes in-waveguide wavelength in the cylindrical waveguide) with respect to the axis direction of the cylindrical waveguide 541. Also, as a unit which exhibits basically the same effect, there exists a unit where one or plural rod-shaped dielectric or dielectrics 591C is or are used in the direction perpendicular to the axis direction of the cylindrical waveguide.
As a conventional embodiment 2, a circularly polarized wave antenna has been disclosed in JP-A-2003-188152. Here, there are provided a cylindrical waveguide and a rectangular waveguide whose one side-surface is connected to the other end of the cylindrical waveguide. Moreover, the circularly polarized wave antenna is provided therebetween. This circularly polarized wave antenna is configured by one slot or plural slots apertured in the cylindrical waveguide on the one side-surface of the rectangular waveguide. This embodiment indicates and describes, as the one slot or plural slots, two slots whose mutual lengths differ from each other and which cross with each other at their centers.
As a conventional embodiment 3, the following method has been disclosed in JP-A-2001-358127: Namely, four power-feeding units are provided on one and the same plane perpendicular to the axis direction of a main coaxial path, and a 90-° phase difference is set between the respective four power-feeding units, then feeding μ waves. Also, this embodiment illustrates a conceptual diagram where the four μ waves with the different phase differences set are distributed from a single μ-wave generation source.